Most backings for carpets are fabrics woven from synthetic yarns. While any number of fabric constructions, yarn configurations and compositions has been utilized or proposed, woven polypropylene tapes, including extruded tapes and slit film, are preferred due to a desirable combination of properties, including tuftability, strength, mold resistance and cost. For some carpets, however, conventional backing fabrics are deficient in one or more respects.
For example, patterned carpets have generally been unavailable or limited to large or irregular patterns due to inadequate dimensional stability of woven tape backings. Shifting and irregular movement of the backings as they advance through a tufting machine result in unacceptable distortion and pattern nonuniformity. Dimensional stabilities of conventional backings typically are 10 lbs. or less and are inadequate for fine patterned carpets. Fabric constructions with many tapes per unit length in the warp and the weft, inclusion of special yarns, and application of coatings or heat sealing to lock the tapes in place have been proposed to increase dimensional stability but they lead to other difficulties. High tape count constructions, e.g., 24×15, 22×24 and 28×15 warp count by weft count, are known and have improved dimensional stability due to greater numbers of tape crossovers per unit area than in lower count fabrics. However, weaving such fabrics is complicated and more costly due to the larger numbers of narrower tapes. In any event, dimensional stabilities of the fabrics do not generally exceed about 30 lbs., whereas stabilities of 50 lbs. or greater would be desirable to promote uniformity in patterned tufting. Coating and heat sealing result in fabrics that are more costly, stiff and difficult to handle. In addition, improvements in dimensional stability resulting from coatings and heat sealing tend to be attained at the expense of tuftability because tufting needles and face yarns are prevented from penetrating the fabrics at the interstices formed by yarn crossovers and, instead, must penetrate through the plastic of the coating and/or the tapes. In high speed tufting, friction between needles and coated or sealed backings can result in heat sufficient to damage face yarns. Use of special yarns may require separate beaming and tension control during weaving, create irregularities in the weave, impede tufting and limit or complicate recycle of fabrics.
As another example, in manufacture of carpet tiles, tufted backing fabrics typically are affixed to a substrate, such as a rubber or vinyl-glass fiber composite substrate. Heating to dry and cure the substrates can involve exposures of the tufted backings to temperatures as high as 300-350° F. for times as long as three to four minutes. As a result of these heat exposures, curling of the tufted backing fabrics can occur. While curling up to about 0.5 to 1 mm is considered tolerable, conventional woven polypropylene backings often curl as much as five to ten mm. Nonwoven polyester fabrics are often used as backings for carpet tiles because polyester softens at temperatures above polypropylene and thus can better withstand heat exposures in tile manufacture. However, polyester backings are more expensive and nonwovens as a rule have dimensional stabilities considerably lower than woven fabrics. Backings woven from tapes composed of polyester or blends thereof with minor amounts of polyolefins such as polypropylene are also known and withstand higher temperatures than woven polypropylene tapes; however, the backings are more costly, polyester tapes are more brittle and backings woven therefrom do not tuft as well as woven polypropylene tape backings.
There is, accordingly, a need for tuftable fabrics having an improved combination of tuftability, dimensional stability and resistance to curling.